Apparatus for improving the reproduction of sound



p 1952 s. D. 'ZIVADINOVICZ 2,612,234

APPARATUS FOR IMPROVING THE REPRODUCTION OF SOUND Filed D90. 5, 1949 I 2 SHEETS- SHEET 56 s. D. 'ZIVADINOVIC Sept. 30, 1952 2,612,234

APPARATUS FOR i PRovINq THE REPRODUCTION OF SOUND Filed We. 5, 1949 2 Sl-IEETS-SHE'ET '2' R Q v. Q

Patented Sept. 30, 1952 APPARATUS FOR IMPROVING THE REPRODUCTION OF SOUND Stevan Dragutin Zivadinovic, Oxford, England Application December 5, 1949, Serial No. 131,133 In Great Britain December 9, 1948 This invention concerns improvements relating to the reproduction of sound by radio receivers, radiograms, extension speakers and like instruments having an enclosed loud speaker. It is a defect of such instruments that the entire sound, whatever its nature, comes from a small localised source inside the cabinet or other enclosure. This is particularly artificial and disturbing in the case of the reproduction of orchestral, choral and like work.

The problem arises from the fact that we possess binaural audition. This does not mean merely that we listen with two ears, but also that there is a psychological achievement which consists in the combination of two different sound sensations into one space perception. Our every-day audition ls three-dimensional and we perceive the positions of, say, musical instruments and their space relation. With music reproduced by a sound-reproducing instrument, however, the original three-dimensional effect is lost, and an artificial source of sound is substituted for all the music emitted by the loudspeaker.

It is an object of the present invention to improve, by simple, compact and practical means, what may be termed the sound picture created by a sound reproducin instrument, and this by producing apparent alterations in the size of the source of sound or apparent locations of the source outside the enclosure of the instrument. In this way, new sound pictures can be produced with marked effects of spaciousness. The sound reproduction can be made more natural and a three-dimensional effect can be achieved, although the effect may not be exactly the same as with direct audition to music in the studio or concert hall.

More specifically it is an object of the invention to provide a simple, compact and practical arrangement in which the main stream of sound from the loud speaker is not directly emittedthrough the front wall of the enclosure, but is only projected to the listening space in front oftheinstrument after reflection from soundreflecting and dispersing means comprising a reflecting screen and at least one discontinuous screen. Accordingly, the loud speakermay be positioned inside an opening in a wall of the enclosure, other than the front wall, and substantially screened on the side towards the said front wall, the principal sound-reflecting and dispersing means being arranged outside the opening.

The invention thus relies mainly upon the 5 Claims. (01. 18131) eifects of reflection and'dispersion. When sound I is reflected from a surface, its apparent source lies behind the surface and its nature depends upon the nature of the surface. A plain smooth surface will give a uniform sound picture with a definite location of the apparent source. Concave and convex surfaces will generally enlarge and reduce respectively the apparent size of the source. A broken or uneven surface, or an openwork screen or other grid in front of the surface, will produce dispersion and an effect of greater spaciousness, the location being less definite. Thus, for instance, the invention may be carried into effect with a measure of success by using as the sound-reflectin and dispersin means an adjustable reflecting screen with an uneven surface. The sound-reflecting and dispersing means may also comprise a grid of rods or other elongated members disposed in front of the screen. Sound dispersion is then assisted by diffraction of the sound waves by the grid members before and after reflection from the screen. In practice, the number of reflections and dispersion effects will preferably be yet further increased by multiplying the number of reflecting screens and/or grids, so that sound waves penetrating between screens are broken up and reflected several times before escaping outside the said screens. Although advantage may be taken of a wall, table or other external refleeting surface to enhance the required effects, the arrangement as a whole should appreciably aifect sound from the loud speaker only and not extraneous sound. v

Use may also be made of resonance effects. Such an effect is produced if an element, for instance a thin paper screen, is set in vibration under the influence of the sound from the loud speaker. The vibrating element itself diffuses sound and the apparent source becomes at least partly identified with it. Although the invention may be carried out with a single effect, provided that this can be altered by adjustment, the use of combinations of eif ects gives a more natural result. Loud speakers have to reproduce the sounds of a range of musical instruments from, say, piccolo to organ. A single effect is bound to give an unnatural result for some instruments when orchestral work is being reproduced. With a combination of selected and properly disposed efiects, however, the sounds of each individual instrument have an opportunity to develop a more natural form. Provision may be made for adjusting the combination of effects, but even a non-adjustable combination of selected effects can give satisfactory results,

A preferred practical embodiment of the invention and various modifications by way of example will now be described with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic side elevation, partly in section, of an arrangement in accordance with the invention applied to a radio receiver,

Figure 2 a front elevation of the receiver,

Figure 3 a rear elevation of the receiver,

Figure 4 a side elevation of the principal sound reflecting and dispersing means to a larger scale.

Figure 5 a plan view of the said means in a folded condition, parts being shown broken away to disclose the rearmost screen.

Figure 6 is a diagrammatic sideelevationillustrating a modified arrangement in the extended condition, and

Figure '7 a similar view in the folded condition.

In the arrangement illustrated in Figures 1-3, a rearwardly directed loud speaker I is disposed towards the rear of the cabinet of the receiver, the opening 2 for the main stream of shun-d being provided in the back wall 3. A second opening 4 through which a smaller stream of sound is to pass is provided in the front wall '5. The opem ing 4 is intended to give a rather sharp frontal apparent location of the sound source. A screen 6 is suspended in or "near the opening 4 to produce some dispersion and to displace the eforesaid location slightly forwardly. It should, nowever, not close the opening or prevent the free flow of sound, so that the loud speaker itself can still be vaguely perceived as a second source of sound, although obscured by the dispersion in the receiver and by the screen it. A suitable screen is of forwardly splayed V' section with a small central round hole lfcFigure 2 "This form of screen assists in providing a result which is fairly uniform over the Whole listening space in front of the receiver. I A

The principal sound reflecting and dispersing "means is disposed immediately behind the opening 2 in the back wall 3 of the receiver. As illustrated in greater detail in Figures '4 and 5, the said means consists in the main of three s'creens and a grid disposed one behind another, although the surf-ace on which the receiver stands End/0'1 a wall behind it may "also play a part as "additional reflecting surfaces. The first "screen, which is smaller than the others and always leaves a considerable portion of thes'econd screen uncovered, consists of two parts -fl, lying fiat against each other in an upwardly inclined .position. The smaller part 8 is fixedly mounted, whereas the other part 9 is adjustable inits own plane, so that the eifectivea-rea of the whole screen can be increased or reduced. In the simple example illustrated, adjustment is effected by turning a cylinder [0 on which are wound tapes H by which the screen part9 is suspended. The main stream of sound from the loudspeaker I is directed substantially at the middle of the fixed screen part 8. The arrangement .is such that when the screen part '9 is raised, theamou-nt of sound reflected at the first screen decreases and that reaching the further screens increases. The screen parts 8, 9 have a number of holes and/or slots arranged so that the opening and closing of free passages through them depends upon the position of the part 9. One "suitable pattern of such holes and slots I 2, I2 is shown in Figure 5. When the screen part 9 is down, passages appear in the lower portion of the screen. When it am-id position, passages 'cally corrugated paper.

appear in the middle and, when it is up, in the upper portion thereof.

The second screen 13, which is inclined at a larger angle, comprises a smooth board divided into three parts by two narrow slots 14 extending from top to bottom. Parts of the sound stream pass to the third screen through these slots and, preferably, also through a gap l5 under the screen l3.

A grid I6 is disposed between the first screen 8, 9 and the second screen l3. It consists of a series of upstanding rods l1 spaced apart at intervals which increase from the middle outwardly. Bars, tubes, strings or like elongated members may take the place of rods and instead ofthe simple grid illustrated use may be made of a grid composed of crossed or interlaced members or formed by a surface with holes through it. Whatever the form of this openwork grid, the area allowing through passage of sound should be substantially larger than the reflecting area.

The third screen [8 is a single vertical board presenting an uneven surface 19 of, say, verti- It may be provided with a window (not shown) which, when open, allows a part of the sound stream to produce a further reflection effect at a wall of the If desired, a further grill or grids may be provided between the second and third screen's I3, l8 or in front of or behind the loud speaker "I. Additional screens may also be provided.

A small vibratory screen 20 is arranged centrally in or near the rear opening 2. This screen, made of thin paper for example, is designed so that it can be set in vibration and itself diffuse sound.

Reflections from the first screen 8, 9, which may also vibrate to some extent, and from the second screen [3' produce a certain amount of dispersion due to the fact that their surfaces are, at least, not highly polished. Much more dispersion is produced by the grid l5, for not only do the rods I1 cause diffraction of the sound, but also numerous reflections, as the reflected sound does not all escape at once. Assisted by the first and second screens, therefore, the grid l6 produces a thick effect. The third screen l'8 producesa general dispersion effect in which the table surface 2|,or an additional base board, may also play apart. Finally a wall behind the receiver may be made to serve as "a 'reilectoro'f the already dispersed sound, giving an effect of considerable depth. The various openings in theseveral elements ensure harmonious blending of the different effects.

Means may be provided for adjusting any of the elements, but it is not necessary for all to be adjustable and the first screen '8, "9 may be the sole or main adjustment means. When the reflecting surface of this screen is a maximum, the dispersion effects of "the elements behind it are reduced and the localizing effect of the elements in front is increased. This setting is most suitable for solo voices and small instruments. The other extreme adjustment, giving the opposite "result, is most suitable for large orchestra-s, choirs and organs. An intermediate adjustment is suitable for the piano and as a general purpose setting. A scale may beprovided in conjunction with the adjustment means :and

-may read in terms of instruments. Another form of adjustment may be provided by mounting the loud speaker in angul'arly adjustable manner.

Preferably, the screens andrgrid rarefconnected together and to the receiver by hinge means of metal or flexible material, so that they can be readily folded into a substantially flat form. As illustrated in Figures 1 and 4, the grid 16 and the screen [8 are hinged to the screen 13 at 22 and 23 respectively. A pivoted strut 24 and a tie 25 serve to hold the grid l6 and screen H3 in the extended condition. The strut may have a plurality of notches 24', permitting of several adjustments of the relative position of the grid it. If an additional base board is provided, it may be arranged to slide into the cabinet over the base thereof.

A combination such as is illustrated in Figures 4 and 5 could also be constructed as a separate unit to be applied to a radio receiver or other sound reproducing instrument of the kind set forth.

The precise arrangement adopted may naturally depend upon the instrument. The radio receiver illustrated in Figures 1-3 has its valves and other components in an upper compartment 34 provided with the usual control knobs 35 and scale 36 on the front wall 5. The lower compartment 3! is substantially open, although some components may be housed there. The opening 4 may be covered by sound-pervious fabric, as may also the rear opening 2. The principal sound-reflecting and dispersing means may also be enclosed by fabric at the top and sides.

Instead of being arranged at the rear of the receiver, the loud-speaker l, the screen 2|] and the principal sound-reflecting and dispersing means may be arranged at the top, bottom or at one or both sides of the receiver, the general direction of reflection being in each case towards the listening space in front of the receiver. If necessary, the reflection of the sound towards the said space may be assisted by providing additional screens or wings at the sides of the sound-refleeting and dispersing means. If the aforesaid means is arranged at the top of the receiver it may be designed to fold down as a cover. If the bottom'disposition is adopted, the receiver may stand on legs.

The cabinet may have other openings in addition to the openings 2, 4 or may be constructed as a cage, preferably covered with fabric. The baffle board in which the loudspeaker is fixed may also have openings in it.

In the modified arrangement shown diagrammatically in Figures 6 and 7, the screen 8, 9, grid I9 and screen l3 are pivoted or hinged at 2B, 21 and 28 respectively between extensions 29 from the base of the receiver cabinet. The elements can be drawn into the folded condition (Figure 7) by means of a link 30 pivotally connected to the screen [3 at 3| and slidably engaging the elements 9 and I6, by means of lugs 32, one end of the link 30 being engaged in a slot 33 in the side wall of the cabinet.

If desired, the invention can be applied in conjunction with an instrument having two or more loud speakers. Sound-reflecting and dispersing means such as have been described will be provided for one or more of the loud speakers which may be separately controllable as regards apparent source as well as volume and quality. The sounds may then be mechanically mixed so that the sources cannot be separated.

I claim:

1. For improving the performance of a soundreproducing instrument comprising a loudspeaker supported inside a cabinet, the combination with the said instrument of sound-reflecting and dispersing means comprising a reflecting screen and at least one discontinuous screen disposed between the said reflecting screen and the loud speaker, which loud speaker, cabinet and sound-reflecting and dispersing means are arranged in relation to each other so that the main stream of sound from the loud speaker is projected to the listening space in front of the instrument only after reflection from the said means, the said screens being hingedly connected to the cabinet so that they can be folded up against a wall of the cabinet when not in use.

2. For improving the performance of a soundreproducing instrument comprising a loud speaker supported inside a cabinet, an arrangement to be disposed facing the loud speaker and comprising a sound-reflecting screen, an interrupted screen disposed in front of and spaced from the said reflecting screen, and a grid disposed in front of and spaced from the said interrupted screen, the said screens and grid being connected to gether by hinge means so that they can be folded up when out of use.

3. An arrangement according to claim 2 and comprising also a screen disposed in front of the grid and. provided with means for the adjustment of its effective area.

4.. For improving the performance of a soundreproducing instrument comprising a loud speaker supported inside a cabinet, the combination with the said instrument of sound-reflecting and dispersing means positioned opposite to the loud speaker and hingedly connected to the cabinet and comprising a reflecting screen and at least one interrupted screen disposed between the firstnamed screen and the loud speaker, whereby the said reflecting and dispersing means can be folded up against the said cabinet.

5. For improving the performance of a soundreproducing instrument comprising a loud speaker supported inside a cabinet, an arrangement to be disposed facing the loud speaker and comprising a sound-reflecting screen and an interrupted screen disposed in front of the soundrefiecting screen and consisting of at least three panels separated by narrow gaps which extend in the up and down direction in the interrupted screen, the interrupted screen being hingedly connected to the sound-reflecting screen, whereby the screens can either be set in a spaced operative position with the interrupted screen in a slanting position or be folded up in substantially flat form.

STEVAN DRAGU'I'IN ZIVADINOVIC.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,572,387 Harrison Feb. 9, 1926 1,675,102 Holland June 26, 1928 1,761,745 Pomeroy June 3, 1930 1,865,735 Wolff -1 July 5, 1932 1,975,604 Hanson Oct. 2, 1934 2,050,575 Krause Aug. 11, 1936 2,114,680 Goldsmith Apr. 19, 1938 2,124,575 Karnes July 26, 1938 FOREIGN PATENTS Number Country Date 325,273 Great Britain Feb. 17, 1930 

